Robert McGwier wrote: > Thanks for all the comments but I still have my doubts. I am more like > to believe in clock leakage and DAC nonlinearities causing this than I > am with square wave harmonic activity. I will investigate further with > the spec-an if I have time. >
When the aliasing happens with an ADC it can be though of as an impulse train (impulses at the sampling points) being multiplied by the signal. This is the same as convolution in the frequency domain, resulting in the aliasing behavior. With a DAC, it is not a pulse train, but a zero-order hold (aka boxcar filter, sinc, etc). Thus the aliases (more properly, alternate images) are weighted by a sinc function, causing them to get weaker as they get to higher Nyquist zones. It is about 18 dB down in the second zone, for example. Matt _______________________________________________ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio